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HUG-H BODMAN, OF EDGEWOOD, PENNSYLVANIA, ASSIGNOR T0 RODMAN CHEMICALCOMPANY, OF VERONA, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

CASE-HABDENING MATERIAL.

No Drawing.

To all whom it may concern:

Be it known that I, HUGH RODMAN, a'c1t1- zen of the United States, and aresident of Edgewood, in the county of Allegheny and State ofPennsylvania, have made a new and useful Invention in Case-HardeningMaterial, of which the following is a specification.

This invention relates to case-hardenin and discloses a new and improvedcase-har ening material and method of using that material.

It is old to use coking coal in making I case-hardening material. Thisis generally done by crushmgthe coal to a fine powder, mixing withpowdered energizing materlals, coking the mixture to produce large lumpsof impregnated coke and then crushing these lumps and screening tosecure smaller lumps of about one-quarter inch in through dimen- Anothermethod followed on a commercial scale is to mix powdered coking coal andenergizing material with binding material and fashion therefrom smallmasses which will remain as individual small masses when they are heatedto a coking or carburizing temperature. a v

Each of these methods of using coking coal as a base for the manufactureof casehardening material has been commercially utilized andsatisfactory material obtained. It is-to be observed, however, thatmaterial made by either method, as well as any carburizin material inthe form of small lumps as distinguished from dust) is liable todisintegrate somewhat in service, especially when subjected to repeatedre-use, and to make dust, which is not only difficult to handle but alsoreduces the efliciency of the carburizing material. It is generalractice to screen out this dust as forme entailing loss of material andlabor.

I have observed that case-hardening material containing raw, unheatedmaterial (raw bone as. against charred bone, coal as against coke) aremore energetic than the same material after heating, which fact Iattribute to the gases evolved at low temper atures when these rawmaterials are heated with energizing materials in the presence ofSpecification of Letters Patent.

Patented Oct. '7, 1919.

Application med June 16, 1917. Serial No. 175,236.

t e dust if deadding fresh carburizing material to previously usedcarburizing material is the ordinary practlce 1n most shops, and isgenerallydone after the used material has been cooled down from 'itscarburizing heat;

therefore, the use of this scheme in the process I am descr1bing entailsno special effort. I find that when some of my coking coal mixture isadded to previously used mate-- rial and the resultant mixture is usedin carburizing operations the coking coal will coke or frltthepreviously used material together ust enough to insure, a tyin togetherof the dust, but not enough to hinder the easy removal of the steelparts and not enough to cause any warping of the steel- In this way Isecure several valuable improvements in the carburizing of steel. First,I am enabled to use the very cheap carburizing agent consisting of amixture of crushed coking coal and energizers. Second, I secure the highefficiency due to'the use of raw coal rather than to coke. Third, Iovercome the tendency of the carburizing material to form dust. Fourth,I produce a material of high 'thermal conductivity due, I believe, tothe light fritting of the entire mass. Fifth, I overcome the tendency ofsome materials to stick or adhere to the steel after the material hasbeen used. Sixth, I prevent the shrinkage in volume which most materialsundergo when highly heated. The raw coal mixture seems to insure a cleansurface even when mixed with used material which would, alone, ruin thesurface of the steel parts.

It is apparent that the permissible amount of coal mixture which can beadded to the used material will depend upon the nature of the usedmaterial and also upon the coking strength of the coal mixture. I findthat, using the preferred coal mixture which I will describe later on,and adding this to carburizing material which has been secured throughprevious repeated additions of coal mixture, about twenty to thirty percent. of

coal mixture will give excellent results. In

- dust, by adding about twenty-five per cent. of the coal mixture to theused material each time it has been cooled down after a carburizingheat. I find that thismay be conveniently done bv shoveling the twomaterials together, as concrete is mixed, on the ,lloor, but specialmixing devices can, of course, be used if desired.

4 The coal mixture can be varied within wide limits and still insureexcellent results, but I have found the following to give satis- 1factory results and prefer it because of its cheapness and large supply.I crush a good grade of Pittsburgh seam coking coal so it will pass ascreen having eight wires to the linear inch and mix with this twelveand one-half per cent. of powdered soda ash (sodium carbonate) andtwenty. parts of calcium carbonate, each by weight. To this mixture Ithen add ten per cent. (based upon the weight of the coal) of fuel oilso as to "lay the dust. I find that this amount of oil will also beenough to lay the dust of the mixture when this coal/ mixture is later.mixed with the used material. Other proportions of energizer and coalmay be used,

and other energizers such as barium carbo nate may be used.

In adding the coal mixture to the used material for the first time it isnecessary to use some care, as less coal mixture can be added to largesize granular material than to material. consisting largely of smallparticles and dust. If too much coal mixture is used the mass of mixedmaterial will fit together more solidly than is desired ;and of course,if the coal mixture is used alone it will coke to a solid coke, firmlyembedding the metal parts and probably warping them. Where it isnecessary to begin carburizing operations without a supply of used ma-j.terial, I prefer to start with material having a coke base (though othermaterials may be used) and to screen this so 'it will pass through ascreen having about ten wires to the linear inch and to remove all ormost of the fine dust. When the coal mixture is added to this in theproportion of about mums would, if mixed with previously usedcarburizing material in proper proportions, frit or coke the usedmaterial to a light and desirable amount and bind the dust as alreadydescribed. Such materials, would I believe, come within the scope ofthis invention, and they may be termed strongly coking material, sincethey like the Pittsburgh seam coking coal, are characterized by the factthat in coking they form a solid structure of considerable mechanicalstrength. In addition to this, the strongly coking quality of thesematerials is such as to cause them when mixed with separate particles ofother noncoking materials, to form a solid or coke like structure whenheated to a coking temperature, but, as stated, I prefer to use ordinarycoking coal because of its cheapness and availability and because I havethoroughly demonstrated its practicability.

It is obvious that the same end could be secured by maintainingsuflicient energizer in the used material, adding more from time to timeas needed, andthen add the coking.

coal or coking. material only, but this is not so satisfactory as themethod described and would be only another way of getting at thematerial with strongly coking material capable of fritting the mass ofpreviously used material together to form a coke like structure whensubjected to a coking temperature.

2. The method of carburizing steel which.

consists in heating the steel part to be carburized to a carburizingtemperature in a mixture of previously used carburizing material and acoking material capable of frit- .ting the mixture together to form acoke like stucture when sub ected to'the carburizing temperature- 3. Themethod of revivifying spent carburizinglnaterial which consists inintimately mixing spent carburizing material with an energizer and acoking material capable of frittlng the separate particles of the masstogether to form a coke like structure when heated to a carburizingtemperature.

4. The method of carburizing steel and revivifying spent carburizingmaterial which consists in packing the steel to be carburized in anapproximately homogeneous mixture of finely divided spent carburizingmaterial and finely divided strongly coking material capable of frittingthe separate particles of the mixture together to form a coke likestructure, and then in subjecting the mixture and the steel to acarburizing heat.

5. Carburizing material comprising a mixture of finely dividedpreviously used carburizing material and crushed coking coal in theproportions of approximately three parts of used material to one part ofcoal.

7 6. A carburizing material comprising a mixture of about three parts ofpreviously used carburizing material, and one part crushed coking coal,and an energizer.

7 The method of carburizing steel which consists in heating it in amixture of previously used carburizing material and a strongly cokingmaterial containing coking coal.

'8. The method of carburizing steel which consists in heating it in amixture of previously used carburizing material and a strongly cokingmixture of coking coal and an energizer.

9. The method of carburizing steel which consists in heating it in amixture of previously used carburizing material and a strongly cokingmixture containing coking coal, soda ash and calcium carbonate.

10. A carburizing material comprising a mixture of previously usedcarburizing material, crushed strongly coking material and an energizer.

In testimony whereof, I have hereunto subscribed my name this 13 day ofJune, 1917.

HUGH RODMAN.

Witnesses:

R. L. KENT, ANNA CLOHERTY.

